1. Field of the Invention
The present invention pertains to methods for selective diversion in a deviated wellbore and in particular, methods of closing a specific group of perforations in a deviated well casing while leaving the remaining perforations in the well casing open and in communication with the formation.
2. Description of the Prior Art
It is common practice in drilling oil and gas wells to deviate the wellbore from the vertical. When the wellbore is intentionally deviated from the vertical, it is called directional drilling. Directional drilling has application in several situations such as: to obtain production from inaccessible locations, such as populated areas, hostile environments, under rivers, etc.; drilling from offshore platforms; and sidetracking a vertical wellbore after the original well drilled into water or downhole problems require abandonment of the lower wellbore.
It is common practice in completing oil and gas wells, including deviated wells, to set a string of pipe, known as casing, in the well and to pump cement around the outside of the casing to isolate the various formations penetrated by the well. To establish fluid communication between each hydrocarbon bearing formation and the interior of the casing, the casing and cement sheath are perforated at the location of each formation. The perforations within each formation are normally made at 0.degree., 90.degree., 120 .degree. and 180.degree. phasing.
At various times during the life of the well, it may be desirable to temporarily or permanently close off a specific group of perforations in a portion of the casing which are communicating with a certain zone or formation. For example, in water injection wells, it is desirable to permanently close off the specific group of perforations communicating with the most permeable zone after the water in that zone has broken through into the production well. Further, in some cases, it may be desirable to temporarily close off the specific group of perforations communicating with a first zone which is adjacent to a water leg while performing a fracturing treatment on a second zone which is located away from the water leg. There are other situations in which it is desirable to selectively close a specific group of perforations communicating with a particular zone while leaving open the remaining perforations in the casing which communicate with other zones.
One prior method of selective diversion is disclosed in U.S. Pat. No. 4,194,561. This method involves the use of placement devices for positioning buoyant ball sealers at a specific location within the wellbore. These devices are equipped with means to prevent the upward migration of the buoyant ball sealers past the placement device. The ball sealers are seated on the perforations by flowing fluid down the casing and through the device. These devices are normally used to selectively close the perforations located at the lowermost region of the casing.
Therefore, there still exists the need for readily enabling the selective closing of a specific group of perforations located anywhere along the length of the casing.